Many different chemical, biochemical, and other reactions are sensitive to temperature variations. Examples of thermal processes in the area of genetic amplification include, but are not limited to, Polymerase Chain Reaction (PCR), Sanger sequencing, etc. The reactions may be enhanced or inhibited based on the temperatures of the materials involved. Although it may be possible to process samples individually and obtain accurate sample-to-sample results, individual processing can be time-consuming and expensive.
One approach to reducing the time and cost of thermally processing multiple samples is to use a device including multiple chambers in which different portions of one sample or different samples can be processed simultaneously. When multiple reactions are performed in different chambers, however, one significant problem can be accurate control of chamber-to-chamber temperature uniformity. Temperature variations between chambers may result in misleading or inaccurate results. In some reactions, for example, it may be critical to control chamber-to-chamber temperatures within the range of ±1° C. or less to obtain accurate results.
The need for accurate temperature control may manifest itself as the need to maintain a desired temperature in each of the chambers, or it may involve a change in temperature, e.g., raising or lowering the temperature in each of the chambers to a desired setpoint. In reactions involving a change in temperature, the speed or rate at which the temperature changes in each of the chambers may also pose a problem. For example, slow temperature transitions may be problematic if unwanted side reactions occur at intermediate temperatures. Alternatively, temperature transitions that are too rapid may cause other problems. As a result, another problem that may be encountered is comparable chamber-to-chamber temperature transition rate.
In addition to chamber-to-chamber temperature uniformity and comparable chamber-to-chamber temperature transition rate, another problem may be encountered in those reactions in which thermal cycling is required is overall speed of the entire process. For example, multiple transitions between upper and lower temperatures may be required. Alternatively, a variety of transitions (upward and/or downward) between three or more desired temperatures may be required. In some reactions, e.g., polymerase chain reaction (PCR), thermal cycling must be repeated up to thirty or more times. Thermal cycling devices and methods that attempt to address the problems of chamber-to-chamber temperature uniformity and comparable chamber-to-chamber temperature transition rates, however, typically suffer from a lack of overall speed—resulting in extended processing times that ultimately raise the cost of the procedures.
One or more of the above problems may be implicated in a variety of chemical, biochemical and other processes. Examples of some reactions that may require accurate chamber-to-chamber temperature control, comparable temperature transition rates, and/or rapid transitions between temperatures include, e.g., the manipulation of nucleic acid samples to assist in the deciphering of the genetic code. See, e.g., T. Maniatis et al. Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Laboratory (1982). Nucleic acid manipulation techniques include amplification methods such as polymerase chain reaction (PCR); target polynucleotide amplification methods such as self-sustained sequence replication (3 SR) and strand-displacement amplification (SDA); methods based on amplification of a signal attached to the target polynucleotide, such as “branched chain” DNA amplification; methods based on amplification of probe DNA, such as ligase chain reaction (LCR) and QB replicase amplification (QBR); transcription-based methods, such as ligation activated transcription (LAT) and nucleic acid sequence-based amplification (NASBA); and various other amplification methods, such as repair chain reaction (RCR) and cycling probe reaction (CPR). Other examples of nucleic acid manipulation techniques include, e.g., Sanger sequencing, ligand-binding assays, etc.
One common example of a reaction in which all of the problems discussed above may be implicated is PCR amplification. Traditional thermal cycling equipment for conducting PCR uses polymeric microcuvettes that are individually inserted into bores in a metal block. The sample temperatures are then cycled between low and high temperatures, e.g., 55° C. and 95° C. for PCR processes. When using the traditional equipment according to the traditional methods, the high thermal mass of the thermal cycling equipment (which typically includes the metal block and a heated cover block) and the relatively low thermal conductivity of the polymeric materials used for the microcuvettes result in processes that can require two, three, or more hours to complete for a typical PCR amplification.
One attempt at addressing the relatively long thermal cycling times in PCR amplification involves the use of a device integrating 96 microwells and distribution channels on a single polymeric card. Integrating 96 microwells in a single card does address the issues related to individually loading each sample cuvette into the thermal block. This approach does not, however, address the thermal cycling issues such as the high thermal mass of the metal block and heated cover or the relatively low thermal conductivity of the polymeric materials used to form the card. In addition, the thermal mass of the integrating card structure can extend thermal cycling times. Another potential problem of this approach is that if the card containing the sample wells is not seated precisely on the metal block, uneven well-to-well temperatures can be experienced, causing inaccurate test results.
Yet another problem that may be experienced in many of these approaches is that the volume of sample material may be limited and/or the cost of the reagents to be used in connection with the sample materials may also be limited and/or expensive. As a result, there is a desire to use small volumes of sample materials and associated reagents. When using small volumes of these materials, however, additional problems related to the loss of sample material and/or reagent volume through vaporization, etc. may be experienced as the sample materials are, e.g., thermally cycled.
Another problem experienced in the preparation of finished samples (e.g., isolated or purified samples of, e.g., nucleic acid materials such as DNA, RNA, etc.) of human, animal, plant, or bacterial origin from raw sample materials (e.g., blood, tissue, etc.) is the number of thermal processing steps and other methods that must be performed to obtain the desired end product (e.g., purified nucleic acid materials). In some cases, a number of different thermal processes must be performed, in addition to filtering and other process steps, to obtain the desired finished samples. In addition to suffering from the thermal control problems discussed above, all or some of these processes may require the attention of highly skilled professionals and/or expensive equipment. In addition, the time required to complete all of the different process steps may be days or weeks depending on the availability of personnel and/or equipment.
One example is in the preparation of a finished sample (e.g., purified nucleic acid materials) from a starting sample (e.g., a raw sample such as blood, bacterial lysate, etc.). To obtain a purified sample of the desired materials in high concentrations, the starting sample must be prepared for, e.g., PCR, after which the PCR process is performed to obtain a desired common PCR reaction product. The common PCR reaction product must then be prepared for, e.g., Sanger sequencing, followed by performance of the Sanger sequencing process. Afterwards, the multiplexed Sanger sequencing product must be demultiplexed. After demultiplexing, the finished Sanger sequencing product is ready for further processing. This sequence of events may, however, have occurred over days or even weeks. In addition, the technical nature of the processes requires highly skilled personnel to obtain accurate results.
Approaches at using disc-based devices to integrate various thermal processing steps into a single device suffer from a number of disadvantages including the use of high cost silicon substrates and the incorporation of high cost heating and/or cooling systems built into the discs. As a result, the cost of the discs can be prohibitive to their widespread use. See, e.g., International Publication Nos. WO 98/07019 (Kellog et al.); WO 99/09394 (Hubbard et al.).